A copper alloy for electronic materials that are used in a connector, switch, relay, pin, terminal, lead frame, and various other electronic components is required to satisfy both high strength and high electrical conductivity (or thermal conductivity) as basic characteristics. In recent years, as high integration and reduction in size and thickness of an electronic component have been rapidly advancing, requirements for copper alloys used in these electronic components have been increasingly becoming severe.
Because of considerations related to high strength and high electrical conductivity, the amount in which precipitation-hardened copper alloys are used has been increasing, replacing conventional solid-solution strengthened copper alloys typified by phosphor bronze and brass as copper alloys for electronic components. With a precipitation-hardened copper alloy, the aging of a solution-treated supersaturated solid solution causes fine precipitates to be uniformly dispersed and the strength of the alloys to increase. At the same time, the amount of solved elements in the copper is reduced and electrical conductivity is improved. For this reason, it is possible to obtain materials having excellent strength, spring property, and other mechanical characteristics, as well as high electrical and thermal conductivity.
Among precipitation hardening copper alloys, Cu—Ni—Si copper alloys commonly referred to as Corson alloys are typical copper alloys having relatively high electrical conductivity, strength, and bending workability, and are among the alloys that are currently being actively developed in the industry. In these copper alloys, fine particles of Ni—Si intermetallic compounds are precipitated in the copper matrix, thereby increasing strength and electrical conductivity.
Various technical developments have been made with the aim of further improving the characteristics of Corson alloys, including the addition of alloy elements other than Ni and Si, the removal of elements that negatively affect characteristics, the optimization of the crystal structure, and the optimization of precipitating particles.
For example, it is known that characteristics are improved by adding Co.
It is disclosed in Japanese Laid-open Patent Application 11-222641 (Patent Document 1) that Co is similar to Ni in forming a compound with Si and increasing mechanical strength, and when Cu—Co—Si alloys are aged, they have slightly better mechanical strength and electrical conductivity than Cu—Ni—Si alloys. The document also states that, where acceptable in cost, Cu—Co—Si and Cu—Ni—Co—Si alloys may be also selected.
Japanese Domestic Republication No. 2005-532477 (Patent Document 2) describes a tempered copper alloy comprising, in terms of weight, 1% to 2.5% nickel, 0.5 to 2.0% cobalt, and 0.5% to 1.5% silicon, with the balance being copper and unavoidable impurities, and having a total nickel and cobalt content of 1.7% to 4.3% and an (Ni+Co)/Si ratio of 2:1 to 7:1. The tempered copper alloy has electrical conductivity that exceeds 40% IACS. Cobalt in combination with silicon is believed to form a silicide that is effective for age hardening in order to limit crystal grain growth and improve softening resistance. When the cobalt content is less than 0.5%, the precipitation of the cobalt-containing silicide as second-phase is insufficient. In addition, when a minimum cobalt content of 0.5% is combined with a minimum silicon content of 0.5%, the grain size of the alloy after solution treatment is maintained at 20 microns or less. It is described in the document that when the cobalt content exceeds 2.5%, excessive second-phase particles precipitate, formability is reduced, and the copper alloy is endowed with undesirable ferromagnetic properties.
International Publication Pamphlet WO2006/101172 (Patent Document 3) discloses a dramatic improvement in the strength of a Co-containing Cu—Ni—Si alloy under certain compositional conditions. Specifically, a copper alloy for an electronic material is described in which the composition is about 0.5 to about 2.5 mass % of Ni, about 0.5 to about 2.5 mass % of Co, and about 0.30 to about 1.2 mass % of Si, with the balance being Cu and unavoidable impurities, the ratio of the total mass of Ni and Co to the mass of Si ([Ni+Co]/Si ratio) in the alloy composition satisfies the formula: about 4≦[Ni+Co]/Si≦about 5, and the mass concentration ratio of Ni and Co (Ni/Co ratio) in the alloy composition satisfies the formula 0.5≦Ni/Co≦about 2.
It is also disclosed that in solution treatment, it is effective to set the cooling rate to about 10° C. or greater per second because the strength-enhancing effect of the Cu—Ni—Si copper alloy is further demonstrated when the cooling rate after heating is intentionally increased.
It is also known that coarse inclusions in the copper matrix are preferably controlled.
Japanese Laid-open Patent Application 2001-49369 (Patent Document 4) discloses that a material capable of being used as a copper alloy for an electronic material can be provided by adjusting the components of a Cu—Ni—Si alloy; adding as required Mg, Zn, Sn, Fe, Ti, Zr, Cr, Al, P, Mn, Ag, and Be; and controlling and selecting manufacturing conditions to control the distribution of precipitates, crystallites, oxides, and other inclusions in the matrix. Specifically described is a copper alloy for an electronic material that has excellent strength and electrical conductivity, the alloy being characterized in that there are contained 1.0 to 4.8 wt % of Ni and 0.2 to 1.4 wt % of Si, with the balance being Cu and unavoidable impurities; the size of the inclusions is 10 μm or less; and the number of inclusions having a size of 5 to 10 μm is less than 50 per square millimeter in a cross-section parallel to the rolling direction.
Since coarse crystallites and precipitates of an Ni—Si alloy are sometimes formed in the solidification process during casting in semi-continuous casting, the document furthermore describes a method for controlling such a phenomenon. It is stated that “coarse inclusions are solved in the matrix by being heated for 1 hour or more at a temperature of 800° C. or higher, hot-rolled, and then brought to an end temperature of 650° C. or higher. However, the heating temperature is preferably kept at 800° C. or higher and less than 900° C. because problems are presented in that thick scales are formed and cracking occurs during hot rolling when the heating temperature is 900° C. or higher.”    [Patent Document 1] Japanese Laid-open Patent Application 11-222641    [Patent Document 2] Japanese Domestic Republication No. 2005-532477    [Patent Document 3] International Publication Pamphlet WO2006/101172    [Patent Document 4] Japanese Laid-open Patent Application 2001-49369